It is difficult to design switchable 0°/180° phase shifters in the context of microwave monolithic integrated circuits (MMICs), because cost factors often limit the size of the chip that can be used, which in turn limits the available surface area on which circuit structures can be defined. In addition, modern phase shifters may require broad bandwidth, minimal losses, and small phase and amplitude imbalance across the band, which tends to exacerbate the design problem.
The prior art includes switched-line, high-pass/low-pass, loaded-line, and rat-race types of phase shifters. Each has it its own advantages and disadvantages. Improved switchable 0°/180° phase shifters are desired.